1. Field of the Invention
The present invention relates generally to a method and system for vapor deposition, such as Metalorganic Chemical Vapor Deposition (MOCVD). More specifically, the invention relates to a method and system for vapor deposition for epitaxial growth of a semiconductor layer, such as a thin compound semiconductor layer, on a substrate.
2. Description of the Background Art
Recently, epitaxial growth of semiconductor layers, such as thin compound semiconductor layers, is regarded as an important technology for producing high efficiency semiconductor devices. This is especially so, since it is not possible in the conventional art to produce semiconductor devices utilizing a hetero-junction, such as laser diode, a high electron mobility field effect transistor (HEFT), a hetero-junction bipolar transistor (HBT), and other AlGaAs system semiconductor devices, except by a vapor deposition process, and especially a MOCVD process.
During an epitaxial growth process, growth parameters, such as composition of grown layer, growth speed and so forth preferably should be monitored by way of so-called "in-situ monitoring". However, it has been difficult to perform in-situ monitoring in the conventional epitaxial growth apparatuses including silicon epitaxial growth apparatuses. Therefore, in-situ monitoring has not been performed in the conventionally available apparatus.
In recent years, there has been proposed a reflecting high electron rays diffraction (RHEED) method to monitor the surface of the layer of AlGaAs grown by a molecular beam epitaxial (MBE) method and as a feedback for the growth apparatus. However the proposed method is not regarded as practically applicable. The reason is that, since, in the MBE method, spatial distribution of a molecular beam flux has a high and unique anisotropy requiring rotation of the substrate in order to obtain uniformity of the semiconductor layer surface, and consequently, vibration or swaying of the substrate caused during rotation makes it difficult to perform in-situ monitoring by the RHEED method in which the electron ray is irradiated at a low angle of a few degrees.
On the other hand, in the J. Appln. Phys. 51(3), pp 1599-1602, published on March, 1980, there has been proposed a method of performing in-situ monitoring by Elipsimetric (diffracting beam analysis) method for monitoring GaAlAs-GaAs super lattice epitaxial growth grown by the MOCVD method. This Elipsometric method monitors layer growth and derives information of the layer thickness and the refraction index of the layer and so forth based on phase data of reflected light, by irradiating polarized light toward the growing layer at a low angle. This method is regarded as effective in performing in-situ monitoring, but involves disadvantages in that:
(1) it requires a polarized light inlet window and a reflected light outlet window in the apparatus strictly limiting the construction of the apparatus;
(2) also, in this method, it demands great accuracy in setting of the incident angle of the incident light requiring troublesome alignment adjustments of the entire arrangement including the angle of the sample set on a heating base;
(3) since the polarized light has a low angle of incidence passing through growing gas for a relatively long distance, a high level of noise due to disturbance by the gas is caused;
(4) any slight change of the sample position or vibration will have a large affect on monitoring; and
(5) since the monitoring data is output in the form of phase data, it becomes necessary to utilize a computer for extracting growth parameters therefrom.